Grace and Boyd interview Stanley Heath's son Jason,who tells them that his father and two other policeman were murdered for beating to death a suspect in custody some years earlier. It seems likely that that prisoner was Nicholson's father and Boyd becomes convinced that Nicholson knew the boys' murderer and shielded him,deliberately losing his reports. The team's concern for Sarah grows as Nicholson brings in two sinister detectives to spy on them. Gradually Boyd works out that crooked property developer George Barlow took the orphaned Nicholson under his wing and that Nicholson,out of loyalty,protected the murderer,who was close to Barlow. Boyd is able to use this to effect belated justice but is he too late to save Sarah?